A hybrid vehicle that travels with an engine and a motor generator as power sources is recently known. In such hybrid vehicle, the motor generator is driven by an electric power of a battery to generate power, and uses the rotation of drive wheels and the power of the engine to carry out regenerative power generation at the time of vehicle deceleration to charge the battery.
During the travelling of the vehicle, a charged state (State Of Charge: SOC) of the battery is preferably within a predetermined range, and it is desirable to accurately estimate the changing amount in increase and decrease of the SOC of when travelling on a travel scheduled path ahead to suitably maintain such charged state. The regenerative power generation amount by the motor generator differs depending on an uphill road, a downhill road, a flat road, and the like even at the same vehicle speed, and the changing amount of the SOC differs depending on a gradient of the travelling road. Thus, a technique of predicting the regenerative power generation amount at the time of travelling on the downhill road based on gradient information of the travel scheduled path is conventionally disclosed (e.g., Patent Literatures 1 to 3).